The present invention relates to a pneumatic system for conveying particulate, materials and more particularly to pneumatic conveying ejectors for introducing a flow of pressurized motive gas that provides energy for conveying the particulate solids.
Typically, particulate material that is stored in a hopper or silo or is exiting a manufacturing process is gravity fed into a solids supply vessel or rotary valve airlock and then conveyed through a pipeline to a remote collection site. The pipeline, which is connected to the material outlet at the bottom of the solids supply vessel or rotary valve airlock) is pressurized to within a desired pressure range that provides a pressure differential between the solids supply vessel or rotary valve airlock and the remote collection site suitable to achieve a desired material flow in the pipeline. An ejector may, under certain conditions, replace the solids supply vessel or rotary valve to supply compressed gas (e.g., air) into the pipeline to move the particulate material through the pipeline as it is delivered from the granular solids source.
In certain environments, particulate material is conveyed using a supply of compressed gas having a gauge pressure of 15 psig or less. This low pressure gas is supplied by a suitable low-pressure compressor. Alternately, rather than using a dedicated low-pressure compressor, the plant""s high-pressure (e.g., 80-120 psig) compressed gas source may be used to power the conveying ejector. The high-pressure supply is regulated to a lower pressure before delivery to the ejector.
The present invention improves the efficiency of ejectors for low-pressure pneumatic conveying systems that are powered by gas (e.g., air) from a high-pressure source. In the system of the present invention, the ejector for conveying particulate solids includes two stages, a gas introduction stage and a solids introduction stage. The solids introduction stage connects to the outlet of the source of granular solids to be conveyed and to the pipeline for introducing compressed gas and solids into the pipeline to convey the material flowing from the outlet through the pipeline. The gas introduction stage mixes the high pressure gas from the high-pressure source with air or other suitable gas at atmospheric or low pressure and discharges such mixture into the solids introduction stage.
The gas introduction ejector stage includes a T-shaped or cylindrically shaped fluids mixing chamber with a primary inlet port, an outlet port that is collinear with the primary inlet port, and a transversely located, upper secondary inlet port. The primary inlet port has connected therein a high-pressure compressed gas supply connector, which is in turn connected to a high-pressure source. The outlet port has connected therein a nozzle that provides communication between the gas introduction ejector stage fluids mixing chamber and a similar T-shaped or cylindrically shaped fluids/solids mixing chamber of the solids introduction ejector stage. The secondary inlet port of the gas introduction ejector stage is opened to the atmosphere or other source of suitable low-pressure gas.
In operation, as high-pressure compressed gas enters the gas introduction stage mixing chamber at high velocity, a vacuum is created in the gas introduction stage mixing chamber which draws in atmospheric air or other low-pressure gas from the secondary inlet port. This mixture of compressed gas and atmospheric air/low-pressure gas is discharged at a high velocity into the solids introduction stage fluids/solids mixing chamber through the connecting nozzle. The particulate solids passing from the outlet of the solids supply vessel enter the fluids/solids mixing chamber and are entrained in the high velocity mixture of compressed gas and atmospheric air/low-pressure gas, and the gas/air/suspended solids mixture is conveyed out of the fluids/solids mixing chamber and through the pipeline.
In this manner, the normally wasted energy of the high-pressure compressed gas is used to induce additional mass flow. Inducing additional mass flow by drawing atmospheric air or low-pressure gas in through the secondary inlet port allows a reduction in the amount of high-pressure gas needed to meet the mass flow requirements of the system, thereby saving energy and costs associated therewith.